#include <iostream>
#include <vector>
#include <queue>
#include <stack>
#include <algorithm>
using namespace std;

struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};

class Solution
{
public:
    vector<int> largestValues(TreeNode *root)
    {
        vector<int> res;
        queue<TreeNode *> que;
        if (root) que.push(root);
        while(!que.empty()){
            int size = que.size();
            int max = INT32_MIN;
            while(size--){
                TreeNode * node = que.front();
                que.pop();

                max = node->val > max ? node->val : max;
                if (node->left) que.push(node->left);
                if(node->right) que.push(node->right);
            }
            
            res.push_back(max);
        }
        return res;
    }
};